A high-power device is a semiconductor device for high-voltage/current applications. Examples of high-power devices include a stud/flat diode, a switch, a rectifier, thyristors, etc. High-power devices are used for power plants, railways, ships, automobiles and large power sources that require quality products with high reliability.
Gallium oxide (Ga2O3) is a promising semiconductor material for use in future power devices due to its wide bandgap. The bandgap of gallium oxide ranges from 4.5 electron volts to 4.9 electron volts, as opposed to other popular semiconductor materials, such as silicon with a bandgap of ˜1.1 electron volts, silicon carbide with a bandgap of 3.2 electron volts and gallium nitride with a bandgap of 3.4 electron volts. Gallium oxide is also preferred by the semiconductor industry as high-quality gallium oxide wafers can be manufactured by atmospheric melt growth methods as discussed in “Recent progress in Ga2O3 power device,” Higashiwaki et al., Semiconductor Science and Technology, Vol. 31, No. 3, pp. 034001 (January 2016).
N-type Gallium oxide field-effect transistors are usually normally-on. An n-type normally-on field-effect transistor has a negative threshold voltage and usually conducts current from the source to the drain to even when there is no voltage applied to its gate terminal, resulting in high leakage current. As used herein, a “voltage applied to the gate terminal” and the like means a non-zero voltage across the gate and source terminals. “No voltage applied to the gate terminal” and the like means that the voltage across gate and source is zero. Therefore, an n-type normally-off field-effect transistor is desired which has a positive threshold voltage and does not conduct current from the source to the drain even when there is no voltage applied to its gate terminal. N-type Gallium oxide field-effect transistors also have a low drive current (i.e., a low current between the source and the drain when a voltage is applied to the gate) if the channel is lightly doped or too thin.
In “Enhancement-mode Ga2O3 wrap-gate finFETs on native (100) β-Ga2O3 substrate with high breakdown voltage”, Chabak et al., Applied Physics Letters, Vol. 109, Iss. 21, pp. 213501 (October 2016), the authors describe a normally-off gallium oxide field-effect transistor with very low drive current because of the recess in the middle of the channel.
It is therefore desirable to provide us a gallium oxide field-effect transistor that is normally-off and have a high drive current.